The proposed experiments are designed to examine the way in which the fusional and stereoptic mechanisms achieve single binocular vision in humans with normal binocular function. This knowledge will then be applied to the treatment of binocular deficiency in strabismic patients. My aim is to arrive at a comprehensive description of human fusional response. The results will provide long needed information on: 1. the dynamic characteristics of the motor response, 2. the relative roles the central and motor components play in fusion and stereopsis, 3. the nature and extent of interactions between the fusional and stereoptic mechanisms. These concepts are basic and necessay for the understanding of human binocular vision.